Nano-reagents with cooperative catalysis and their uses in multiple phase reactions

ABSTRACT

Nano-reagents with catalytic activity are provided herein. The nanocatalyst comprises at least one amino acid attached to a nanoparticle, wherein the reactive side chain of the amino acid catalyzes a chemical or biological reaction. Methods of using these nano-reagents to catalyze reactions in solution or in multiple phases are also provided, as are methods of making these nanocatalysts.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 11/668,151 filed Jan. 19, 2007, which claims benefit ofpriority to U.S. Provisional Application Ser. No. 60/763,123 filed Jan.27, 2006, each of which is hereby incorporated by reference in itsentirety.

GOVERNMENTAL RIGHTS

This invention was made with government support under grant numbersCHE-0343440 and CHE-0534321 awarded by the National Science FoundationCAREER Award Program. The Government has certain rights in thisinvention.

FIELD OF THE INVENTION

The present invention provides nano-reagents with catalytic activity andmethods of using these nanocatalysts to catalyze chemical and biologicalreactions.

BACKGROUND OF THE INVENTION

Catalysts are widely used in many industrial applications, such aspharmaceutical and fine chemicals manufacturing. A catalyst may benecessary for a reaction to occur or for the process to be economicallyviable. Many catalysts are expensive because they are made from preciousmetals, such as platinum or palladium, or because of the processingrequired to make a catalyst of a particular size, shape, or crystalphase. Because of the scale of industrial process and the expense of thecatalysts it is desirable to be able to recover and reuse catalysts.Tradition methods of recovery have met limited success, however.

Furthermore, enzymes catalyze some industrially important reactions. Thelimited stability, high substrate specificity, and limited availabilityof sufficient quantities of some enzymes, however, have tended to limittheir use. Thus, a need exists for small, stable, biomimetic catalyststhat also could be recovered and reused.

SUMMARY OF THE INVENTION

Among the various aspects of the present invention is the provision of amethod for making a nanocatalyst comprising at least one reactivespecies attached to a metal oxide nanoparticle. The process comprisesmixing at least one hydroxyl-containing compound carrying the reactivespecies with a metal oxide nanoparticle coated with a hydrophobicsurfactant. During the mixing step the hydroxyl-containing compoundreplaces the hydrophobic surfactant on the surface of the nanoparticle,whereby the nanocatalyst is produced.

Other aspects and features of the invention are detailed below.

DESCRIPTION OF THE FIGURES

FIG. 1 presents schematic diagrams of nanocatalysts of the invention. A.A nanocatalyst comprising a carboxylic acid-containing amino acid(aspartic acid, Asp) attached via a dopamine linker to an iron oxidenanoparticle. B. A nanocatalyst comprising an imidazole-containing aminoacid (histidine, His) attached via a dopamine linker to an iron oxidenanoparticle. C. A nanocatalyst comprising a thiol-containing amino acid(cysteine, Cys) attached via a dopamine linker to an iron oxidenanoparticle. D. A nanocatalyst comprising three different amino acids(Asp, His, Cys) attached via silicon hydroxide linkers to an iron oxidenanoparticle. E. A nanocatalyst comprising two amino acids (Asp, His)attached via dopamine linkers to an iron oxide nanoparticle. F. Ananocatalyst comprising a palladium-containing compound [N-heterocycliccarbene (Pd—NHC)] attached via a silicon hydroxide linker to an ironoxide nanoparticle. G. A nanocatalyst comprising a nanoparticle coatedwith a polymer, with amino acids attached to the polymer. H. Ananocatalyst comprising a nanoparticle coated with a polymer, withpolypeptides attached to the polymer. I. A nanocatalyst comprising ananoparticle coated with a polymer linked to reactive species. J. Ananocatalyst comprising a nanoparticle embedded in a matrix comprisingpolymer to which the reactive species are attached.

FIG. 2 illustrates the surface-exchange reaction during the synthesis ofa nanocatalyst comprising amino acids (AA) attached to an iron oxidenanoparticle. The amino acid-derived dopamine molecules replace theoleic acid molecules on the surface of the nanoparticle.

FIG. 3 diagrams reactions catalyzed by nanocatalysts comprising ironoxide nanoparticles linked to one or two amino acids. The black circlerepresents the nanocatalyst, which was removed by applying an externalmagnet (horseshoe symbol) upon completion of each reaction. A.Hydrolysis of the carboxylic ester bond of paraoxon (diethylp-nitrophenylphosphate). B. Hydrolysis of the phosphoester bond of4-nitrophenyl acetate. C. Hydrolysis of the phosphodiester bond in theRNA construct, UpU. D. Hydrolysis of the phosphodiester bond in the DNAconstruct, dApdT.

FIG. 4 diagrams a solid phase Suzuki coupling reaction catalyzed by amagnetic Pd nanocatalyst (diagramed in FIG. 1F). Substrate X wasimmobilized on the resin, which was contacted with the nanocatalyst andsubstrate B. The magnetic nanocatalyst was removed by applying anexternal magnet. The produce P was released from the resin and purified.

DETAILED DESCRIPTION OF THE INVENTION

A nanocatalyst has been discovered that comprises at least one aminoacid residue attached to a nanoparticle, wherein the reactive side chainof the amino acid catalyzes a chemical reaction. Furthermore, it hasbeen discovered that these nano-reagents also catalyze biologicalreactions that are generally catalyzed by enzymes. The reactive groupsof the amino acid side chains may interact cooperatively to catalyze thereaction, in a manner similar to the active sites of many enzymes. Thereactions catalyzed by these nanocatalysts may be in solution or theymay be in multiple phases. Additionally, nanocatalysts comprising amagnetic nanoparticle may be magnetically separated from the reactionproducts, byproducts, and excess reagents that are in solution or in oneof the orthogonal matrices, such that the nanocatalysts may berecovered, recycled, and reused again.

I. Nanocatalyst

(a) Nanoparticle

One aspect of the present invention provides a nanocatalyst comprising ananoparticle attached to at least one reactive species, whereby thereactive species functions as a catalyst. In one embodiment thenanoparticle may be a magnetic material. Non-limiting examples ofsuitable magnetic materials include a metal, a metal oxide, a metaldioxide, a metallic salt, a metal alloy, an intermetallic alloy, anorganic magnetic material, a derivative thereof, or a combinationthereof. Suitable metals include iron, cobalt, manganese, nickel, or arare earth metal. Alloys are typically combinations of two or morecompounds, of which at least one is a metal. Suitable alloys, therefore,include alloys of iron, alloys of cobalt, alloys of manganese, andalloys of nickel. Intermetallic alloys are generally mixtures of two ormore metals in a certain proportion. Suitable examples of anintermetallic alloy include cementite (Fe₃C), alnico (a blend ofaluminum, nickel, and cobalt), or Ni₃Al. Among the suitable metal oxidesinclude iron oxides, such as magnetite (Fe₃O₄) or maghemite (Fe₂O₃).Other suitable magnetic materials include ferrofluids or spinelferrites. The magnetic material may also be an organic material, such as7,7,8,8-tetracyano-p-quinodimethane or tetrathiafulvaleniumtetracyanoqinomethane. In a preferred embodiment, the nanoparticlecomprises an iron oxide.

In another embodiment, the nanoparticle may comprise a non-magneticmaterial. The non-magnetic material may be inorganic or organic.Suitable examples of an inorganic material include, but are not limitedto, silver, gold, titanium, aluminum, cadmium, selenium, silicon,silica, or mixtures thereof. The inorganic material may be formulatedinto a nanocrystal, a nanosphere, a quantum dot, an electricsemiconductor, and the like. An organic non-magnetic material may be asynthetic polymer, a semisynthetic polymer, or a natural polymer.Non-limiting examples of synthetic organic polymers includepolyacrylate, polyacrylamide, poly(acrylamide sulphonic acid),polyacrylonitrile, polyamine, poly(amidoamine), poly(arylamine),polycarbonate, poly(ethylene glycol), poly(ester), poly(ethylene imine),poly(ethylene oxide), poly(ethyloxazoline), polyhydroxyethylacrylate,polymethacrylate, polymethacrylamide, poly(oxyalkylene oxide),poly(phenylene), poly(propylene imine), poly(propylene oxide),polystyrene, polyurethane, poly(vinyl alcohol), and poly(vinylpyrrolidone). An example of a suitable natural polymer is cellulose andits (semisynthetic) derivatives, such as methylcellulose,carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,and hydroxy-propylmethylcellulose. Other examples of natural polymersinclude polysaccharides or carbohydrate polymers, such as hyaluronicacid, dextran, dextrin, heparan sulfate, chondroitin sulfate, heparin,alginate, agar, carrageenan, xanthan, and guar. The non-magneticmaterial may also be a micelle comprising an aggregate of surfactantmolecules dispersed in a liquid.

One skilled in the art will appreciate that the size of a nanoparticlecan and will vary depending on the nature of the material comprising thenanoparticle and the intended use of the nanocatalyst. The averagediameter of a nanoparticle may range from about 0.01 nanometers (nm) toabout 100,000 nm, preferably from about 0.1 nm to about 1,000 nm, andmore preferably from about 1 nm to about 100 nm. In a preferredembodiment the average diameter of a nanoparticle may range from about 2nm to about 25 nm.

(b) Reactive Species

The nanoparticle is linked to at least one reactive species, whichfunctions as a catalyst. The reactive species may be an acidicfunctional group, a basic functional group, a nucleophilic functionalgroup, or a catalyst atom.

In one embodiment, the reactive species may be an acidic functionalgroup. In general, an acid functional group refers to a proton (H⁺)donor. Examples of acidic groups include, but are not limited to,borate, carboxylate, hydroxamic acid, phenol, phosphoric acid,phosphorous acid, seleninic acid, sulfinate, sulfonate, thiol acid, orderivatives thereof.

In another embodiment, the reactive species may be a basic functionalgroup. In general, a basic functional group refers to a proton (H⁺)acceptor. Examples of basic groups include, but are not limited to,amino groups including primary, secondary and tertiary amines,heterocyclic amines, guanidines, or derivatives thereof.

In yet another embodiment, the reactive species may be a nucleophilicgroup. Generally, a nucleophilic group has an unshared pair ofelectrons, and the group may be neutral or have a negative charge.Examples of nucleophilic functional groups include, but are not limitedto, amide, amino (including primary, secondary, or tertiary amines),borate, carboxylate, guanidine, heterocyclic amine, hydroxyl,hydroxylamine, hydroxamic acid, hydrazine, o-iodosylcarboxylate, phenol,phosphine, phosphine oxide, phosphine sulfide, phosphine sulfoxide,phosphorate, phosphorous acid, seleninic acid, sulfinate, sulfonate,thio, thiol acid, or derivatives thereof. In another aspect of thisembodiment, the nucleophilic group may comprise —X¹—OH (or —X¹—O⁻),—X¹—NH₂, or —X¹—SH (or —X¹—S⁻) structures, where X¹ may be P, I, Br, Cl,B, Al, N, O, S, Se, As, Si, or Ge.

In an alternate embodiment, the reactive species may be a catalyst atom.In general, a catalyst atom is a metal or non-metal that exhibitscatalytic activity. Non-limiting examples of a suitable catalyst atominclude platinum, palladium, iridium, gold, osmium, ruthenium, rhodium,or rhenium. In a preferred embodiment, the catalyst atom forming thereactive species may be palladium.

One skilled in the art will appreciate that the aforementioned reactivespecies may be part of a larger molecule. Essentially, the reactivespecies may be attached to a hydrocarbyl moiety or a substitutedhydrocarbyl moiety. In one embodiment, the reactive species may be partof a larger chemical compound, e.g., palladium N-heterocyclic carbene(Pd—NHC) (see FIG. 1F). In another embodiment, the reactive species maybe part of an amino acid or a polypeptide. In yet another embodiment,the reactive species may be part of a nucleic acid. In still anotherembodiment, the reactive species may be part of a carbohydrate. In apreferred embodiment, the reactive species comprises at least one aminoacid. Amino acids with suitably reactive side chains include asparticacid (Asp), cysteine (Cys), glutamic acid (Glu), histidine (His), lysine(Lys), and serine (Ser) (see FIG. 1A-C).

While at least one reactive species is attached to a nanoparticle,generally many reactive species will be attached to the nanoparticle.For example, a nanoparticle may be surrounded by a shell of reactivespecies. One skilled in the art will appreciate that the number ofreactive species attached to a nanoparticle can and will vary dependingupon the size of the nanoparticle and the density of reactive groups onthe surface of the nanoparticle. The reactive species attached to thenanoparticle may be of the same type. For example, all of the reactivespecies attached to a nanoparticle may comprise acidic groups; they allmay comprise carboxyl groups; they all may comprise palladium; and soforth. Alternatively, the reactive species attached to a nanoparticlemay be of different types. For example, the reactive species attached toa nanoparticle may comprise a mixture of acidic groups and basic groups;they may comprise a mixture of acidic, basic, and neutrophilic groups;they may comprise a mixture of carboxyl groups and imidazole groups;they may comprise a mixture of different amino acids; and so forth.

In a preferred embodiment, a nanocatalyst may comprise a single type ofamino acid. In an exemplary embodiment, a nanocatalyst may comprise twodifferent types of amino acids, selected from the group consisting ofAsp, Cys, Glu, His, Lys, and Ser. In an especially preferred embodiment,a nanocatalyst comprises aspartic acid and histidine attached to ananoparticle (see FIG. 1E). Furthermore, a nanocatalyst may comprisethree or more different amino acids, selected from the group listedabove. In embodiments comprising two or more different amino acids, theamino acids may be attached to the nanoparticle such that their sidechains are positioned in close proximity to each other, whereby thereactive side chains may interact cooperatively to catalyze a chemicalreaction. In particular, the interaction between an acidic group and abasic group on the side chains of two adjacent amino acids maycooperatively catalyze a reaction. Alternatively, the interactionbetween an acidic group and a neutrophilic group on the side chains oftwo adjacent amino acids may cooperatively catalyze a reaction. Theratio of the amino acids attached to the nanoparticle can and will varydepending upon the application. For most applications, however, anequimolar amount of each amino acid may be optimal.

(c) Linkage Between the Reactive Species and the Nanoparticle

Depending upon the embodiment, the reactive species may be attached tothe nanoparticle by a variety of chemical bonds, including but notlimited to, covalent bonding, dative bonding, ionic bonding, hydrogenbonding, or van der Waals bonding. In an exemplary embodiment, thereactive species is attached by a covalent bond.

The reactive species or the compound comprising the reactive species maybe attached directly to the nanoparticle. One skilled in the art willappreciate that the nature of the nanoparticle material will determinethe type of bond utilized for a direct attachment. Alternatively, thereactive species may be attached to the nanoparticle by a linker.Typically, a linker is a molecule having at least two functional groups,such that the linker is disposed between the reactive species and thenanoparticle. Thus, one functional group of the linker forms anattachment with the nanoparticle, and another functional group of thelinker forms an attachment with the reactive species or the compoundcomprising the reactive species. The type of bonds linking the reactivespecies to the nanoparticle via the linker can and will vary dependingupon the reactive species, the linker, and the material of thenanoparticle. Furthermore, the size, length, charge, and/orhydrophilicity/phobicity of the linker can and will vary depending onthe nanoparticle material, the reactive species, and the intended usesof the nanocatalyst.

In a preferred embodiment, the nanoparticle material comprises a metaloxide. A suitable linker comprises a molecule containing at least onehydroxyl group. Without being bound by any particular theory, hydroxylgroups have affinity for the undercoordinated surface sites of the metaloxide. Non-limiting examples of suitable hydroxyl-containing moleculesinclude alcohols, diols, ethendiols, carboxylic acids, and hydroxides.In an especially preferred embodiment, the nanoparticle comprises theiron oxide, maghemite (Fe₂O₃) and the linker comprises the ethenediol,dopamine (4-(2-aminoethyl)benzene-1,2-diol) (see FIG. 1). In anotherespecially preferred embodiment, the nanoparticle comprises maghemiteand the linker comprises silicon hydroxide (see FIG. 1).

In yet another embodiment, the nanoparticle may be coated with apolymer, and the reactive species is attached to the nanoparticle viathe polymer (see FIG. 1H, I). The polymer may be a synthetic polymer, asemisynthetic polymer, or a natural polymer. Suitable polymers werelisted above in section (I)(a). The reactive species may be attacheddirectly to the polymer, via a reactive group in the polymer.Alternatively, the reactive species may be attached to the polymer via alinker, as detailed above.

In still another embodiment, the nanoparticle may be dispersed in atleast one type of polymeric matrix, with the reactive species beingattached to either the nanoparticle or the polymer of the matrix (seeFIG. 1J).

(d) Preferred Embodiments

As detailed above, a nanocatalyst of the invention comprises at leastone reactive species attached to a nanoparticle. Table A lists variouscombinations of nanoparticles and reactive species that formnanocatalysts. Preferred nanocatalysts comprise amino acids withreactive side chains attached to a metal oxide nanoparticle. Anexemplary nanocatalyst comprises equimolar amounts of aspartic acid andhistidine attached to an iron oxide (maghemite) nanoparticle. Anotherexemplary nanocatalyst comprises a palladium-containing compoundattached to an iron oxide (maghemite) nanoparticle.

TABLE A Nanoparticle Material Reactive Species nonmagnetic catalyst atomnonmagnetic palladium nonmagnetic acidic group nonmagnetic basic groupnonmagnetic nucleophilic group nonmagnetic amino acid nonmagnetic Aspnonmagnetic Cys nonmagnetic Glu nonmagnetic His nonmagnetic Lysnonmagnetic Ser nonmagnetic a combination of any two of the following:Asp, Cys, Glu, His, Lys, Ser nonmagnetic Asp, His nonmagnetic acombination of any three of the following: Asp, Cys, Glu, His, Lys, Sermagnetic catalyst atom magnetic palladium magnetic acidic group magneticbasic group magnetic nucleophilic group magnetic amino acid magnetic Aspmagnetic Cys magnetic Glu magnetic His magnetic Lys magnetic Sermagnetic a combination of any two of the following: Asp, Cys, Glu, His,Lys, Ser magnetic Asp, His magnetic a combination of any three of thefollowing: Asp, Cys, Glu, His, Lys, Ser metal oxide catalyst atom metaloxide palladium metal oxide acidic group metal oxide basic group metaloxide nucleophilic group metal oxide amino acid metal oxide Asp metaloxide Cys metal oxide Glu metal oxide His metal oxide Lys metal oxideSer metal oxide a combination of any two of the following: Asp, Cys,Glu, His, Lys, Ser metal oxide Asp, His metal oxide a combination of anythree of the following: Asp, Cys, Glu, His, Lys, Ser iron oxide catalystatom iron oxide palladium iron oxide acidic group iron oxide basic groupiron oxide nucleophilic group iron oxide amino acid iron oxide Asp ironoxide Cys iron oxide Glu iron oxide His iron oxide Lys iron oxide Seriron oxide a combination of any two of the following: Asp, Cys, Glu,His, Lys, Ser iron oxide Asp, His iron oxide a combination of any threeof the following: Asp, Cys, Glu, His, Lys, Ser magnetite (Fe₃O₄)catalyst atom magnetite (Fe₃O₄) palladium magnetite (Fe₃O₄) acidic groupmagnetite (Fe₃O₄) basic group magnetite (Fe₃O₄) nucleophilic groupmagnetite (Fe₃O₄) amino acid magnetite (Fe₃O₄) Asp magnetite (Fe₃O₄) Cysmagnetite (Fe₃O₄) Glu magnetite (Fe₃O₄) His magnetite (Fe₃O₄) Lysmagnetite (Fe₃O₄) Ser magnetite (Fe₃O₄) a combination of any two of thefollowing: Asp, Cys, Glu, His, Lys, Ser magnetite (Fe₃O₄) Asp, Hismagnetite (Fe₃O₄) a combination of any three of the following: Asp, Cys,Glu, His, Lys, Ser maghemite (Fe₂O₃) catalyst atom maghemite (Fe₂O₃)palladium maghemite (Fe₂O₃) acidic group maghemite (Fe₂O₃) basic groupmaghemite (Fe₂O₃) nucleophilic group maghemite (Fe₂O₃) amino acidmaghemite (Fe₂O₃) Asp maghemite (Fe₂O₃) Cys maghemite (Fe₂O₃) Glumaghemite (Fe₂O₃) His maghemite (Fe₂O₃) Lys maghemite (Fe₂O₃) Sermaghemite (Fe₂O₃) a combination of any two of the following: Asp, Cys,Glu, His, Lys, Ser maghemite (Fe₂O₃) Asp, His maghemite (Fe₂O₃) acombination of any three of the following: Asp, Cys, Glu, His, Lys, Ser

II. Method for Using a Nanocatalyst to Catalyze a Chemical Reaction

A further aspect of the invention encompasses methods for using thenanocatalysts of the invention to catalyze chemical reactions. Thesenanocatalysts may catalyze many different types of chemical reactions,but more importantly, these nanocatalysts may catalyze biologicalreactions that are generally catalyzed by enzymes. Furthermore, magneticnanocatalysts may be readily separated and recovered from the reactionmix or the product using an external magnet, such that the nanocatalystmay be recycled and reused.

(a) Types of Reactions

Nanocatalysts may be engineered to catalyze a plethora of chemicalreactions. The chemical reaction may be a combination reaction, adecomposition reaction, or a replacement reaction. Many such reactionsare widely used in industry. Non-limiting examples of such reactionsinclude oxidative-reductive reactions, condensation reactions, couplingreactions, hydrolysis reactions, and dehydration reactions.

It has been discovered that nanocatalysts of the invention may be usedto catalyze the hydrolysis of ester bonds, phosphoester bonds, andphosphodiester bonds (see Example 2). One skilled in the art willappreciate that the hydrolysis of many other types of bonds may becatalyzed by these nanocatalysts. Non-limiting examples of otherhydrolysable bonds include thioester, acyl halide, alkyl halide, arylhalide, amide, acidic anhydride, ether, thioether, phosphohalide,sulfonyl halide, sulfinyl halide, sulfenyl halide, acetal, thioacetal,thioketal, ketal, hemiacetal, thiohemiacetal, hemiketal, thiohemiketal,cyano bonds, and derivatives thereof. Another bond whose hydrolysis maybe catalyzed by these nanocatalysts may be diagrammed as —X²-LG, whereinX² is I C, P, I, Br, Cl, B, Al, N, O, S, Se, As, Si, or Ge and “LG” is aleaving group. A leaving group generally relates to the part of asubstrate molecule that is cleaved and generally has the ability toattract electrons and/or negative charges. Non-limiting examples ofleaving groups include acetate (—OCOCH₃), halogens (—F, —Cl, —Br, and—I), trifluoroactetate (—OCOCF₃), methansulfonate (—O—SO₂CH₃), tosylate(—OSO₂C₆H₄CH₃), nitrosulfonate (—OSO₂C₆H₄NO₂), and triflate (—OSO₂CF₃).

(b) Reaction Conditions

The nanocatalysts of the invention generally function under mildreaction conditions. Traditionally, many chemical reactions areperformed at extreme pH values, elevated temperatures, in the presenceof caustic reagents, toxic organic solvents, and/or heavy metals. Incontrast, reactions catalyzed by the nanocatalysts of the invention aregenerally performed at a neutral pH, a moderate temperature, and in anaqueous solution (see Example 2). Depending upon the application, areaction mixture may further comprise a buffering agent, a cation, asurfactant, an organic solvent, a reducing agent, or a co-reactant. Aswill be appreciated by one skilled in the art, the reactions conditionsand reaction components will vary depending upon the application.

The pH of the reaction may range from about 5.0 to about 9.0, preferablyfrom about 6.0 to about 8.0, and more preferably at about 6.5 to about7.5. The temperature of the reaction may range from about 20° C. toabout 80° C., preferably from about 25° C. to about 65° C., and morepreferably from about 30° C. to about 45° C. The duration of thereaction may range from about 1 hour to about 96 hours, preferably fromabout 6 hours to about 72 hours, and more preferably about 12 hours toabout 48 hours. In one embodiment, the pH of the reaction may be about6.5 to about 7.5, the temperature of the reaction may be about 25° C. toabout 30° C., and the duration of the reaction may be about 24 hours toabout 48 hours. In yet another embodiment, the pH of the reaction may beabout 6.5 to about 7.5, the temperature of the reaction may be about 37°C., and the duration of the reaction may be about 24 hours to about 48hours.

The efficiency of the nanocatalyst, which may be assessed as the percentof conversion of the substrate to the product, will generally be atleast 50%. The percent of conversion may be about 60%, 70%, 80%, 85%,90%, 95%, or 99%. Preferably, the percent of conversion may be at least75%.

(c) Recovery of the Nanocatalyst

Magnetic nanocatalysts may be separated from the reaction mixture or theproduct by applying an external magnet. Thus, the nanocatalyst may bereadily recovered, concentrated, recycled, and reused repeatedly. Theproduct of the reaction may be isolated and/or purified from thereaction mixture by a variety of techniques well known in the art.

(d) Applications

In one embodiment, a nanocatalyst of the invention may be used tocatalyze the hydrolysis of an environmental pollutant, whereby theenvironmental pollutant is inactivated. The environmental pollutant maybe a pesticide, an insecticide, an herbicide, or an insect repellent.Non-limiting examples of environmental pollutants include paraoxon,parathion, methyl parathion, malathion, methoprene, DEET, atrazine,azinophos-methyl, diazinon, O-chlorobenzylmalononitrile, and derivativesthereof (see Table B). The environmental pollutant may be in surfacewater, ground water, or the soil. Alternatively, the environmentalpollutant may not be dispersed in the environment but may still be inneed of inactivation (e.g., in a storage facility). Thus, a nanocatalystof the invention may hydrolyze and inactivate the environmentalpollutant in water, soil, or another medium at ambient temperatures.Additional reagents, such as divalent cations, may be also be added.Upon completion of the reaction, a magnetic nanocatalyst may berecovered magnetically from the reaction medium, recycled, and reused.

TABLE B Common Chemical Structure Name Chemical Name

Paraoxon (diethyl p-nitrophenylphosphate)

Parathion (diethyl p-nitrophenyl monothiophosphate)

Methyl parathion (dimethyl p-nitrophenyl monothiophosphate)

O-chlorobenzyl-malononitirile

Malathion ([(dimethoxyphosphinothioyl)thio] butanedioic acid, diethylester)

Methoprene ((E,E)-11-methoxy-3,7,11- trimethyl-2,4-do-decadienoic acid,1-methylethyl ester)

DEET (N,N-diethyl-3-methylbenzamide)

Atrazine (2-chloro-4-ethylamino-6- isopropyl-amine-s-triazine)

Azinphos- methyl (phosphorodithioic acid, O,O- dimethyl S-[(4-oxo-1,2,3-benzotriazin-3(4H)-yl)methyl]ester)

Diazinon phosphorothioic acid O,O-diethylO-[6-methyl-2-(1-methylethyl)-4- pyrimidinyl] ester

In an alternate embodiment, a nanocatalyst of the invention may be usedto catalyze the hydrolysis or inactivation of a chemical warfare agent.Non-limiting examples of chemical warfare agents include Sarin,Lewisite, Soman, Tabun, VX, chloroacetophenone (ClC₆H₄COCH₃),bromobenzylcyanide (BrC₆H₄CH₂CN), and derivatives thereof. These andother examples of chemical warfare agents are presented in Table C. Asdescribed above for the environmental pollutants, a nanocatalyst mayinactivate a chemical warfare agent in water or soil under mild reactionconditions. Furthermore, a magnetic nanocatalysts may be magneticallyrecovered and recycled.

TABLE C Common Chemical Structure Name Chemical Name

Sarin (GB) (methylphosphonofluoridic acid 1-methylpropylester)

Lewisite dichloro((E)-2- chlorovinyl)arsine

Soman (GD) (methylphosphonofluoridic acid, 1,2,2- trimethylpropylester)

Tabun (GA) (dimethylphosphoramido- cyanidic acid, ethyl ester)

VX (methylphosphonothioic acid, S-[2-[bis-(1- methylethyl)amino]-o-ethylester])

cyclohexyl methylphosphonofluoridate (GF)

phosphonofluoridic acid, ethyl-, isopropyl ester (GE)

Phosphonothioic acid, ethyl- S-(2-(diethylamino)ethyl) O- ethyl ester

Amiton S-2-(diethylamino)ethyl O,O-diethyl phosphorothioate

VM S-2-(diethylamino)ethyl O- ethyl methyl- phosphonothioate

Russian VX S-2-(diethylamino)ethyl O- isobutyl methyl- phosphonothioate

(ethylbis(2- chloroethyl)amine)

Mechloreth- amine (2-chloro-N-(2-chloroethyl)- N-methylethanamine)

Trichlormethine (tris(2-chloroethyl)amine)

Dichloroformo- xine hydroxycarbonimidic dichloride

diphenylcyanoarsine

cyanogen chloride ≡N hydrogen cyanide Cl—Cl chlorine

trichloronitromethane

Diphosgene (trichloromethyl chloroformate)

methyldichloroarsine

phosgene

Sulfur Mustard (1,1′-thiobis(2- chloroethane))

(1-(2-(2-(2- chloroethylthio)ethoxy)- ethylthio)-2-chloroethane)

ethyldichloroarsine AsH₃ Arsine (arsenic trihydride)

In still another embodiment, a nanocatalyst of the invention may be usedto catalyze the hydrolysis of esters in chemical industrial processes.As an example, a magnetic nanocatalyst may be utilized in an industrialsaponification process. In general, industrial saponification refers tothe hydrolysis of a fatty acid ester into an alcohol and the salt of acarboxylic acid (also called a soap). Generally, vegetable oils andanimal fats, which are primarily triglycerides comprising glycerolesterified with three fatty acids, are the starting materials.Typically, an industrial saponification process is performed in thepresence of a strong base (NaOH or KOH) and heat. The products comprisefree glycerol and fatty acid salts. A nanocatalyst of the invention maybe used to catalyze the hydrolysis of the triglycerides at a neutral pHand at a moderate temperature in the presence of a cation. A magneticnanocatalyst may be recovered and reused.

In yet another embodiment, a nanocatalyst of the invention may be usedto catalyze the hydrolysis of a phosphodiester bond in a nucleic acid.The nucleic acid may comprise deoxyribonucleotides or ribonucleotides,or a combination thereof. The nucleic acid may be single-stranded ordouble-stranded. Non-limiting examples of ribonucleic acids (RNA)include messenger RNA (mRNA), micro RNA (miRNA), short interfering RNA(sRNA), and viral RNA. The hydrolysis of a phosphodiester bond in anucleic acid may be targeted to a specific sequence by also attaching anoligonucleotide, whose sequence is complementary to the sequence of thetarget nucleic acid, to the nanoparticle. Thus, the oligonucleotideattached to the nanoparticle may hybridize with the target nucleic acid,such that the reactive species attached to the nanoparticle catalyzesthe hydrolysis of a phosphodiester bond in the target nucleic acid.

The oligonucleotide attached to the nanoparticle may comprisedeoxyribonucleotides, ribonucleotides, or a combination thereof. Thenucleotides comprising the oligonucleotide may be standard nucleotidesor non-standard nucleotides, and the nucleotides may be modified orderivatized nucleotides. The nucleotides may be linked by phosphodiesterbonds or non-hydrolysable bonds, such as phosphorothioate ormethylphosphonate bonds. The oligonucleotide may also comprisemorpholinos, which are synthetic molecules in which bases are attachedto morpholino rings that are linked through phosphorodiamidate groups.The oligonucleotide may also comprise alternative structural types, suchas peptide nucleic acids (PNA) or locked nucleic acids (LNA). The lengthof the oligonucleotide may range from about 4 nucleotides to about 30nucleotides, and more preferably from about 8 nucleotides to about 18nucleotides.

As detailed above, the nucleic acid hydrolysis reactions may beperformed under mild conditions. The reactions may be performed invitro. The reactions may also be performed in vivo, for example, inhumans, animals, or plants. The method may further comprise an initialheating step to denature the target nucleic acid, such that the targetnucleic acid may hybridize with the oligonucleotide attached to thenanoparticle. Upon completion of the reaction, the method may furthercomprise another heating step to denature and release the cleavedproduct from the oligonucleotide attached to the nanoparticle. Magneticnanocatalysts may be recovered and reused, as described above. Oneskilled in the art will appreciate the applications of this embodiment.For example, a nanocatalyst may be targeted to cleave a viral RNAmolecule, such as HIV-1 tar RNA. Further, nanocatalysts may beengineered for use in antisense therapies for disease treatments.

(III) Method for Using a Nanocatalyst to Catalyze a Multiple PhaseReaction

Yet another aspect of the present invention provides methods for usingthe nanocatalysts of the invention to catalyze multiple phase reactions.Multiple phase reactions may comprise two phases, wherein a firstreagent is immobilized on a matrix and a second reagent is immobilizedon a nanoparticle. Alternatively, multiple phase reactions may comprisethree phases, wherein a first reagent is immobilized on a matrix, asecond reagent is immobilized on a nanoparticle, and a third reagent iseither in solution or immobilized on a second matrix. One skilled in theart will appreciate that multiple phase reactions may also comprise fourphases, five phases, and so forth.

The composition of the matrix can and will vary depending upon theapplication and the reaction being catalyzed. The matrix may comprise asynthetic solid phase resins, such as 1-2% divinylbenzene crosslinkedpolystyrene and its derivatives, or non-crosslinked polystyrene and itsderivatives. The matrix may also comprise a synthetic or a semisyntheticpolymer, as detailed above in section (I)(a). Another suitable polymeris a ROMP gel, which is synthesized by ring-opening metathesispolymerization reactions. The matrix may comprise sol-gels, which areporous materials consisting of inorganic oxides such as silica, alumina,zirconia, stannic or tungsten oxide, or mixtures thereof. Sol-gels thatcontain uniform pore dimensions are generally termed monolithicsol-gels. The matrix may also comprise aerogels, which are porousmaterials consisting of inorganic oxides such as silica, alumina,zirconia, stannic or tungsten oxide, or mixtures thereof. The pores ofaerogels are usually filled with air instead of solvents and water. Thematrix may also comprise silica gels, glass beads, zeolites, graphites,or derivatives thereof. Lastly, the matrix may also comprise fluorotags,which usually refer to organic functionalities or molecules containingmultiple fluoro atoms or polymers that have multiple fluoro atoms.Examples of molecules containing fluorotags are4-[3-(perfluorooctyl)propyl-1-oxy]benzyl alcohol andbis[diphenyl-[4-(1H,1H,2H,2H-perfluorodecyl)phenyl]phosphine]palladium(II) chloride. Both molecules contain a C₈F₁₇ group.

A wide variety of chemical reactions may be performed using multiplephase technologies. Non-limiting examples include coupling reactions,condensation reactions, replacement reactions, dehydration reactions,and hydrolysis reactions. In particular, multiple phase reactions may beused to synthesize many different types of molecules. For example,biopolymers (i.e., polypeptides, nucleic acids), synthetic polymers,small organic molecules, etc. may be synthesized in multiple phases.Thus, the nanocatalysts of the invention, rather than traditionalcatalysts, may be used in a variety of multiple phase chemicalreactions.

In one embodiment, the method comprises contacting a nanocatalyst with asubstrate immobilized on a matrix. The nanocatalyst comprises at leastone reactive species attached to a nanoparticle, whereby the reactivespecies catalyzes the reaction to generate a product. The product may beimmobilized on the matrix or the product may be in solution. If thenanocatalyst is magnetic, then the nanocatalyst may be magneticallyseparated from the matrix and the product, such that the nanocatalystmay be recycled and reused.

In another embodiment, the method further comprises contacting thenanocatalyst and the immobilized first substrate with a secondsubstrate. The second substrate may be in solution or the secondsubstrate may be immobilized on a second matrix. As an example, thereaction may be a Suzuki cross-coupling reaction (see Example 4). Forthis reaction, the first substrate that is immobilized on a matrix maybe an aryl halogen, and the second, soluble, substrate may be anarylboronic acid. The nanocatalyst may comprise palladium (i.e., Pd—NHC)attached to a metal oxide nanoparticle (see Example 3). The reaction maybe performed at pH values that range from about 6.0 to about 9.0. Thetemperature of the reaction may range from about 20° C. to about 100° C.The duration of the reaction may range from about 1 hour to about 10days. In a preferred embodiment, the pH of the reaction may be about7.0, the temperature of the reaction may be about 80° C., and theduration of the reaction may be about 6 days.

IV. A Process for Making a Nanocatalyst

Still another aspect of the present invention encompasses a method formaking a nanocatalyst comprising at least one reactive species attachedto a metal oxide nanoparticle. The method comprises mixing onehydroxyl-containing compound carrying the reactive species with a metaloxide nanoparticle coated with a hydrophobic surfactant. During themixing step, the hydroxyl-containing compound replaces the hydrophobicsurfactant on the surface of the metal oxide nanoparticle, thus formingthe nanocatalyst (see Example 1 and Example 3).

The hydroxy-containing compound may be an alcohol, a diol, an ethenediol(e.g, dopamine), a carboxylic acid, or a hydroxide. In a preferredembodiment, the hydroxy-containing compound may be dopamine. In anotherpreferred embodiment, the hydroxy-containing compound may be siliconhydroxide.

The reactive species may be an amino acid with a reactive side chain,such as aspartic acid, cysteine, glutamic acid, histidine, lysine, andserine. The reactive species may also be a compound containing acatalyst atom, such as palladium. Methods known in the art may be usedto couple the reactive species-containing compound to thehydroxy-containing compound.

The hydrophobic surfactant coating the metal oxide nanoparticle may be asaturated long chain fatty acid, an unsaturated long chain fatty acid,or a mixture thereof. The fatty acid may comprise from about 14 carbonsto about 22 carbons. In a preferred embodiment, the hydrophobicsurfactant may be oleic acid. The metal oxide nanoparticle may be aniron oxide, such as magnetite (Fe₃O₄) or maghemite (Fe₂O₃).

The process comprises mixing the derivatized hydroxyl-containingcompound and the coated nanoparticle. The mixing may comprise sonicationfor a period of time. The time may range from about 0.5 hour to about 15hours, preferably from about 2 hours to 10 hours, and more preferablyabout 6 hours. During the mixing step the hydroxyl-containing compoundsreplace the oleic acid molecules coating the surface of thenanoparticle, such that the hydroxyl-containing compounds becomeattached to the surface of the nanoparticle.

DEFINITIONS

To facilitate understanding of the invention, a number of terms aredefined below:

The term “alkyl” embraces linear, cyclic or branched hydrocarbonradicals having one to about twenty carbon atoms or, preferably, one toabout twelve carbon atoms. Examples of such radicals include methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,pentyl, iso-amyl, hexyl and the like.

The term “alkenyl” embraces linear or branched hydrocarbon radicalshaving at least one carbon-carbon double bond of two to about twentycarbon atoms or, preferably, two to about twelve carbon atoms. Examplesof alkenyl radicals include ethenyl, propenyl, allyl, propenyl, butenyland 4-methylbutenyl.

The term “alkynyl” denotes linear or branched carbon or hydrocarbonradicals having at least one carbon-carbon triple bond of two to abouttwenty carbon atoms or, preferably, two to about twelve carbon atoms.Examples of such radicals include propargyl, butynyl, and the like.

The term “aryl” as used herein alone or as part of another group denoteoptionally substituted homocyclic aromatic groups, preferably monocyclicor bicyclic groups containing from 6 to 12 carbons in the ring portion,such as phenyl, biphenyl, naphthyl, substituted phenyl, substitutedbiphenyl or substituted naphthyl.

A “catalyst” refers to a substance that enables a chemical or biologicalreaction to proceed at a faster rate or under different conditions (asat a lower temperature) than otherwise possible. The catalyst itself isnot consumed during the overall reaction.

“Complimentary” refers to the natural association of nucleic acidsequences by base-pairing (5′-A G T-3′ pairs with the complimentarysequence 3′-T C A-5′). Complementarity between two single-strandedmolecules may be partial, if only some of the nucleic acids pair arecomplimentary, or complete, if all bases pair are complimentary.

The term “heterocyclic” as used herein alone or as part of another groupdenote optionally substituted, fully saturated or unsaturated,monocyclic or bicyclic, aromatic or nonaromatic groups having at leastone heteroatom in at least one ring, and preferably 5 or 6 atoms in eachring.

The term “hydrocarbyl” as used herein describe organic compounds orradicals consisting exclusively of the elements carbon and hydrogen.These moieties include alkyl, alkenyl, alkynyl, and aryl moieties. Thesemoieties also include alkyl, alkenyl, alkynyl, and aryl moietiessubstituted with other aliphatic or cyclic hydrocarbon groups, such asalkaryl, alkenaryl and alkynaryl. Unless otherwise indicated, thesemoieties preferably comprise 1 to 20 carbon atoms.

The term “hybridize” refers to the process of annealing, base pairing,or hydrogen bonding between the nucleotides of two single strandednucleic acids.

The term “hydrolyzing” or “hydrolyze” or “hydrolysis” refers to achemical process of decomposition involving the splitting of a bond andthe addition of the hydrogen cation and the hydroxide anion of water orthe alkoxide or aryloxide anion of an alcohol or the thiolate ion of athiol alcohol.

The term “linker” as used herein refers to a molecule with at least twofunctional groups, such that the linker is disposed between the reactivespecies (or a compound containing the reactive species) and thenanoparticle.

The term “nucleic acid,” as used herein, refers to sequences of linkednucleotides. The nucleotides may be deoxyribonucleotides orribonucleotides. The nucleic acid may be single-stranded ordouble-stranded.

The term “oligonucleotide” refers to a short nucleic acid, i.e., lessthan about 50 nucleotides.

A “polymer” is a chemical compound or mixture of compounds consistingessentially of repeating structural units. Polymers include, but are notlimited to natural, synthetic, and semi-synthetic polymers.

The “substituted hydrocarbyl” moieties described herein are hydrocarbylmoieties which are substituted with at least one atom other than carbon,including moieties in which a carbon chain atom is substituted with ahetero atom such as nitrogen, oxygen, silicon, phosphorous, boron,sulfur, or a halogen atom. These substituents include halogen,carbocycle, aryl, heterocyclo, alkoxy, alkenoxy, alkynoxy, aryloxy,hydroxy, protected hydroxy, keto, acyl, acyloxy, nitro, amino, amido,nitro, cyano, thiol, ketals, acetals, esters and ethers.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples that follow representtechniques discovered by the inventors to function well in the practiceof the invention. However, those of skill in the art should, in light ofthe present disclosure, appreciate that many changes can be made in thespecific embodiments that are disclosed and still obtain a like orsimilar result without departing from the spirit and scope of theinvention, therefore all matter set forth or shown in the accompanyingdrawings is to be interpreted as illustrative and not in a limitingsense.

EXAMPLES

The following examples illustrate various embodiments of the invention.

Example 1 Synthesis of Iron Oxide Nanoparticle-Amino Acid Complexes

Chemicals and organic solvents mentioned below were purchased fromAldrich (Milwaukee, Wis.) or Acros Organics (Pittsburgh, Pa.) and usedas received. Water was obtained from a Milli-Q water system purchasedfrom Millipore Corporation (Milford, Mass.). The heavy metal andbacterial contaminant levels in Milli-Q water were below 10 parts perbillion. Permanent magnets were purchased from Dexter MagneticTechnologies Inc. (Elk Grove Village, Ill.).

To generate amino acid-linked nanocatalysts, amino acids with acarboxylate, a basic or a nucleophilic group on the side chain, such asAsp, Glu, His, and Lys, were attached to dopamine(4-(2-aminoethyl)benzene-1,2-diol) using standard procedures (OrganicLetters 2006, 8, 3215). The α-amino groups of the amino acids wereacylated to mimic the amide bonds of the enzyme backbones.Exchange-replacement reactions were conducted by mixing 0.06 mmol of anamino acid dopamine derivative in 1 mL of CHCl₃ and 1 mL of methanolwith 60 mg of ˜12-nm maghemite (Fe₂O₃) nanoparticles coated with oleate(Nature Mater. 2004, 3, 891; J. Colloid Interface Sci. 2003, 258, 427).For nanoparticles coated with two amino acids, 0.03 mmol of each aminoacid residue was utilized in the exchange reaction. The mixture wassonicated for 6 h. The reaction is diagrammed in FIG. 2. Magneticnanoparticles were magnetically concentrated and washed with CH₂Cl₂ (20mL×4) and methanol (20 mL×4) sequentially.

Example 2 Catalysis of Phosphoester, Carboxylic Ester, andPhosphodiester Bonds by Iron Oxide Nanoparticle-Amino Acid Complexes

The maghemite nanoparticle-amino acid complexes prepared in Example 1were used to catalyze hydrolysis reactions using paraoxon (diethylp-nitrophenylphosphate), 4-nitrophenyl acetate, an RNA construct (UpU),or a DNA construct (dApdT) as substrates (FIG. 3). The general procedureinvolved introducing a nanocomplex (amino acid concentration 0.06 mM) toa solution of substrate (0.5 mM) in 2 mL of Milli-Q water at 37° C.After 48 h, the nanocomplex was magnetically concentrated and removedfrom the solution (Org. Lett. 2006, 8, 3215). The solution was thensubjected to HPLC analyses using an internal standard for the conversionyield of the substrate. The structures of the hydrolytic products wereconfirmed by LC-MS experiments. Each experiment was repeated at leasttwo times.

The hydrolysis of the phosphoester bond of paraoxon (FIG. 3A) by thedifferent nanoparticle-amino acid complexes is presented in Table 1.Nanoparticles coated with Asp and His analogues (Fe₂O₃-Asp-His) (Entry8, Table 1) exhibited the highest catalytic activity. For example, after48 h, 77% of paraoxon was hydrolyzed using Fe₂O₃-Asp-His; after 96 h, aconversion yield of 92% was achieved. In contrast, a mixture of Asp andHis without a nanoparticle support (Entry 20) led to a conversion yieldof less than 1%. Within the margin of experimental error, theunsupported amino acid pair showed no catalytic activity in thehydrolysis of paraoxon. On the other hand, the nanoparticle supportitself does not appear to be a catalyst, as entry 1 showed that after 48h less than 1% of paraoxon was hydrolyzed by maghemite nanoparticleswithout a shell of amino acid coatings. Nanoparticles protected withother dyad pairs of amino acids (Entries 9-19, Table 1) were less activecatalysts than Fe₂O₃-Asp-His. For example, the nanocomplex with Glu andHis led to a conversion yield of 51% after 48 h (Entry 12), which islower than that of a dyad of Asp and His despite the fact that thestructures of Asp and Glu are similar to each other. Kinetic studiessuggested that the hydrolysis of paraoxon by Fe₂O₃-Asp-His fits into theMichaelis-Menten model. Analysis of the Lineweaver-Burk plot gaveK_(M)=1.1 mM and k_(cat)=4.3×10⁻⁵s⁻¹ in a pH 7.4 buffer at 40° C. forFe₂O₃-Asp-His. The Fe₂O₃-Asp-His nanocomplex was also used to catalyzethe hydrolysis of paraoxon at ambient temperature (25° C.), and it wasfound to be about 10-fold slower than at 37° C.

TABLE 1 Cleavage of Paraoxon by 12 nm Maghemite Nanoparticle-SupportedAmino Acids Conversion Entry Amino Acid Yield (%) 1 Nanoparticle^(a) <12 Asp  5 3 Cys 15 4 Glu <1 5 His  6 6 Lys  2 7 Ser  4 8 Asp + His77/92^(b) 9 Asp + Lys 27 10 Asp + Cys 25 11 Asp + Ser 28 12 Glu + His 5113 Glu + Lys 50 14 Glu + Cys 44 15 Glu + Ser 45 16 His + Cys 30 17 His +Ser 40 18 Lys + Ser 17 19 Lys + Cys 39 20 Asp, His^(c) <1 ^(a)12 nmmaghemite nanoparticles coated with oleate (no amino acids attached).^(b)Reaction time: 96 h. ^(c)Un-supported Asp (0.14 mM) and His (0.14mM) and paraoxon (0.5 mM) in 2 mL of Milli-Q water at 37° C. for 48 h.

Table 2 presents the cleavage of the carboxylic ester bond of4-nitrophenyl acetate (FIG. 3B) by the nanoparticle-amino acidcomplexes. Most of the nanocomplexes coated with pairs of amino acidswere effective catalysts (Entries 8-18, Table 2), with conversion yieldsgenerally greater than 50%. The Fe₂O₃-Cys-Lys, Fe₂O₃-Lys-Ser, andFe₂O₃-Asp-His nanocomplexes had the highest catalytic activity of 84%,76%, and 67%, respectively. Nanoparticles coated with oleic acid and noattached amino acids (Entry 19) had no catalytic activity.

TABLE 2 Cleavage of 4-Nitrophenyl Acetate by 12 nm MaghemiteNanoparticle- Supported Amino Acids Conversion Entry Amino Acid Yield(%) 1 blank <1 2 Asp 30 3 Cys 27 4 Glu 12 5 His 24 6 Lys 19 7 Ser 28 8Asp + His 67 9 Asp + Ser 54 10 Asp + Lys 54 11 Cys + His 57 12 Cys + Glu54 13 Glu + Lys 56 14 Glu + Ser 55 15 Cys + Lys 84 16 His + Ser 54 17Lys + Ser 76 18 Glu + His 10 19 Nanoparticle- <1 oleate^(a)^(a)p-nitrophenyl acetate (1 mM) and maghemite nanoparticles coated witholeate (no amino acid residues on the surfaces) (2 mg) in 2 mL of pH 7.4phosphate buffer (0.05 mM) at 35° C. for 12 h.

RNA or DNA constructs were exposed to the Fe₂O₃-Asp-His nanocomplex asdetailed above. This nanocomplex completely hydrolyzed thephosphodiester bond of UpU (FIG. 3C) and dApdT (FIG. 3D).

Example 3 Synthesis of Iron Oxide Nanoparticle-Pd Complexes

To make the Pd-containing nanocomplexes, about 60 mg of 11-nm γ-Fe₂O₃nanocrystals coated with oleate in 50 mL of chloroform was treated with(3-chloropropyl)trimethoxysilane (1 mL, 5.48 mmol). The resultingsolution was then brought to reflux. After 12 h, the solution was cooleddown to ambient temperature. Nanoparticles were magneticallyconcentrated by using an external permanent magnet and washed withtoluene (2×50 mL), 0.1 M HCL (2×50 mL) and methanol (2×50 mL). Theresulting nanoparticles were air-dried. Such nanoparticles werere-dissolved in 45 mL of dry toluene and then N-methylimidazole (0.75mL, 9.41 mmol) in 5 mL of toluene was added. The resulting solution wasbrought to reflux and after 16 h, it was cooled down to roomtemperature. Nanoparticles were then magnetically concentrated andwashed with toluene, HCl and methanol sequentially.

About 100 mg of the aforementioned magnetic nanoparticles werere-dissolved in a mixture of DMF (2 mL) and Na₂CO₃ aqueous solution (0.5M, 2 mL) in the presence of Pd(OAc)₂ (22 mg, 98 μmol). After 16 h at 50°C., the mixture was cooled down to room temperature. The nanoparticle-Pdcomplexes were magnetically concentrated and washed with water (3×50mL), 0.1 M HCl (3×50 mL), methanol (3×50 mL) and air-dried. The amountof Pd on the nanoparticles was determined via elemental analysis. TEMmeasurements and elemental analyses were employed for the structure ofIron Oxide-Pd.

Example 4 Use of Iron Oxide-Pd Complexes in Solid Phase SuzukiCross-Coupling Reactions

The reaction scheme is presented in FIG. 4. A typical solid-phase Suzukicross-coupling reaction was as follows. First, a solid phase polystyreneresin (1% divinylbenzene crosslinked, 200-400 mesh) was loaded with arylhalogens (J. Org. Chem. 2006, 71, 537). Then, the aforementioned resin(1.22 g) loaded with an aryl halogen (1 mmol) was added to a mixedsuspension of the arylboronic acid (2 mmol) and K₂CO₃ (2 mmol) in 20 mLof DMF containing Iron Oxide-Pd (4 nm) (30 mg, 0.87 mol %). The mixturewas heated to 80° C. and was maintained at this temperature for 6 days.Iron Oxide-Pd was magnetically concentrated using an external permanentmagnet. To this end, the mixture was vigorously shaken. A permanentmagnet was then applied externally. Magnetic nanoparticles wereconcentrated on the sidewalls of the tube (horizontal direction) whilesome resins were suspended in solution or precipitate at the bottom ofthe tube (vertical). The suspended and precipitated resins, as well asthe solution, were transferred out of the tube using a pipette. Thisprocess usually needed to be repeated more than eight times to ensurethat most of nanoparticles were removed from resins. Iron Oxide-Pd wasthen washed with methanol (10×200 mL). Afterwards, magneticnanoparticles were further washed with water (5×100 mL) and methanol(5×100 mL). The nanoparticles were then air-dried and used directly fora new round of Suzuki reaction.

The resins and excessive arylborate were separated via filtration. Thebeads were recovered as the filter and subsequently washed with methanol(5×100 mL) and water (5×100 mL). The cleavage of the Suzuki product outof the resins was achieved by adding the solid-phase beads (1.18 g) andNaOH (2 mmol) to a mixture of ethanol (15 mL) and water (15 mL). Themixture was heated to reflux and stirred at this temperature for 2 days.After cooling down to ambient temperature, resins were filtered off andthe filtrate was neutralized with 1 M HCl to pH 7. Solvents were removedin vacuo and the residues were extracted with ethyl acetate (10×50 mL).The combined organic solutions were dried over anhydrous Na₂SO₄ andsubjected to HPLC and NMR analyses. A simple recrystallization step wasalso employed using EtOH/H₂O to improve the purity of the Suzukiproduct. The structures of isolated Suzuki products were determined by¹H NMR, IR and high-resolution MS. HPLC analyses of isolated productsafter recrystallization showed that high purity (>99%) was obtained. AUV detector with a fixed wavelength of 254 nm was employed for signaldetection. A typical HPLC analysis program used a solvent gradientstarting from 40% H₂O in CH₃CN to 10% H₂O in CH₃CN in 6 min followed by10% H₂O in CH₃CN for additional 9 min with a flow rate of 0.5 mL/min.

The yields of the solid-phase cross-coupling products were summarized inTable 3. The Iron Oxide-Pd nanocomplex effectively catalyzed thesereactions.

TABLE 3 Suzuki Cross-Coupling of Aryl Halogens (on Resins) andArylboronic Acids (in Solution) under Iron Oxide-Pd (4 nm). Suzukiproduct^(b) entry Y^(a) borate yield (%)^(c) purity (%)^(d) 1 o-I

78 >99 2 o-I

63 >99 3 o-I

71 >99 4 o-I

77 >99 5 o-Br

62 >99 ^(a)See FIG. 4, Y = substitution on phenyl ring. ^(b)Suzukiproducts were cleaved from resins and purified via recrystallizationsteps. ^(c)Average of at least two runs. ^(d)Purity was determined byHPLC analyses and the structures of Suzuki products were confirmed by ¹HNMR and MS.

1. A process for making a nanocatalyst comprising at least one reactivespecies attached to a metal oxide nanoparticle, the process comprisingmixing at least one hydroxyl-containing compound carrying the reactivespecies with a metal oxide nanoparticle coated with a hydrophobicsurfactant, whereby the hydroxyl-containing compound replaces thehydrophobic surfactant on the surface of the metal oxide nanoparticleand the nanocatalyst is produced.
 2. The process of claim 1, wherein themixing comprises sonication for about six hours.
 3. The process of claim1, wherein the hydrophobic surfactant is chosen from a saturated longchain fatty acid, an unsaturated long chain fatty acid, and a mixturethereof, the fatty acid comprising about 14 to about 22 carbons.
 4. Theprocess of claim 1, wherein the hydroxyl-containing compound is chosenfrom an alcohol, a diol, a carboxylic acid, and a hydroxide.
 5. Theprocess of claim 1, wherein the reactive species is an amino acid chosenfrom aspartic acid, cysteine, glutamic acid, histidine, lysine, andserine.
 6. The process of claim 1, wherein the reactive species is apalladium-containing compound.
 7. The process of claim 4, wherein themetal oxide nanoparticle is an iron oxide nanoparticle, the hydrophobicsurfactant is oleic acid, and the hydroxyl-containing compound isdopamine.
 8. The process of claim 7, wherein the reactive species is anamino acid chosen from aspartic acid, cysteine, glutamic acid,histidine, lysine, and serine.
 9. The process of claim 4, wherein thewherein the metal oxide nanoparticle is an iron oxide nanoparticle, thehydrophobic surfactant is oleic acid, and the hydroxyl-containingcompound is silicon hydroxide.
 10. The process of claim 9, wherein thereactive species is a palladium-containing compound.